Most familial congenital deafness is inherited as an autosomal recessive trait. Heterogeneity is high, and to date 39 non-syndromic recessive loci have been identified (Van Camp et al., 1997). Twenty causally related genes have been cloned that encodes proteins with a wide range of functions (Van Camp and Smith, 2003). Interestingly and unexpectedly, mutations in GJB2 at the DFNB1 locus are responsible for half of severe-to-profound autosomal recessive non-syndromic deafness (ARNSD) in many world populations, making DFNB1 the most common type of hereditary congenital hearing loss (Green et al., 1999; Zelante et al., 1997). These discoveries have several important consequences. First, the identification of genes essential for normal auditory function is providing insight into inner ear physiology at the molecular level. Second, the ability to recognize specific types of genetic deafness has made comparative studies of genotype, phenotype and habilitative outcome feasible. And third, the use of genetic testing to diagnose ARNSD has changed the medical evaluation of the deaf person. This competing continuation will continue to focus on these areas by addressing specific aims: 1) To identify novel ARNSD genes; (2) To define genotype-phenotype associations in persons with DFNB1 deafness; (3) To study Pendred syndrome as a complex disease, focusing on the role of FOXI1 and its interacting partners in the Pendred syndrome phenotype.